I use "British journal of political science" citation style, which quotes in the footnote as a direct quote like German. My professor advises me to use a footnotes citation style in English with "cf." or "see". Is there any styles which add automaticly cf. to as indirect selected quotations?

In your citation style you can tell Citavi to automatically insert "cf." or "see" in front of indirect quotations. Open the style in the Citation Style Editor and click File > Citation style properties > Quotation affixes . Enter the prefix you want to use in the "Indirect quotation" fields.

If you have not been saving quotations in Citavi, you might want to insert "cf." or "see" in front of a reference inserted into your document. In the Word Add-In, select the reference you want and then click Insert advanced. Enter "cf." or "see" in the Prefix field. You can also add "cf." or "see" later on by selecting the citation on the Citations tab and then entering the prefix in the Prefix field.